The distance between a mudline hanger and a seat in the wellhead on which the hanger, at the upper end of the string, is to be landed is fixed. It is necessary to adjust the effective vertical spacing between the hangers at opposite ends of the string in some way in order to suspend it in tension. Various solutions have been proposed to this problem in the past. One is the use of short lengths of "pup" joints in the casing and another solution has been to cut the casing string at the wellhead and suspend the cut end from split-type hangers as is frequently done in the case of land-type completions. Such techniques are time consuming and costly, particularly in off-shore installations.
U.S. Pat. No. 4,794,988 discloses a hanger body which includes a vertically adjustable component. The upper portion is adapted to land on the seat in the head and the lower portion is connected to the upper end of the casing string. During installation a shoulder on the upper part is initially above and then lowered on to the seat in order to support the string and tension. This design required a hanger body of complex and expensive construction and further required the wellhead to be taller than would necessarily be required for a conventional installation. Prior solutions have not offered the use of a straight-threaded longitudinally adjustable sub in the string beneath the hanger because of frequent requirements to rotate the string in opposite directions.
U.S. Pat. No. 4,995,464 illustrates an adjustable sub which is manipulated by a tool lowered through the hanger body and into the sub so as to adjust it from an extended position in which its shoulder is above the seat in the head to a retracted position in which the shoulder is seated on the head and the casing string is placed in tension. The operation of this device is disclosed in FIGS. 2 and 3 of U.S. Pat. No. 4,995,464. A sleeve 23 disposed between tubular members 21 and 22. The tubular members 21 and 22 are, rotationally locked by lug 24. The sleeve 23 has opposite hand threads on an inner and an outer surface to match corresponding threads on the tubular members 21 and 22. Rotation of the sleeve 23 translates the tubular 21 and the sleeve 23 downwardly to land the shoulder on the seat in the head. The disadvantages of the design in U.S. Pat. No. 4,995,464 are that the sleeve 23 is difficult to manufacture and operate.
Also relevant in this field are U.S. Pat. Nos. 4,408,783; 4,465,134; 4,653,589; 4,653,778; 4,726,425; 4,239,083; 4,634,152; 4,674,576; 4,714,111; 4,719,971; 4,823,871; 4,836,288; 5,176,218; 5,439,061; 5,607,019; 5,638,903; 5,653,289; 4,757,860.
U.S. Pat. No. 5,524,710 illustrates the use of external grooves and a dog which is insertable into the grooves to maintain tension on the string off of a seat or support shoulder in the wellhead.
U.S. Pat. Nos. 4,938,289 and 4,794,988 illustrate the use of a lock-ring device to retain tension on the string off of a seat or support in the wellhead after tension is pulled on the string.
Finally, U.S. Pat. No. 5,878,816 shows the same technique as illustrated in U.S. Pat. No. 5,524,710 of putting dogs in grooves to retain tension held on the string so that the string is supported off a support surface in the wellhead for retaining the tension.